Chapter 7, Communications, Chapter 7: communications – Watlow Series F4S/D User Manual

Page 77: Chapter seven: communications, Overview

Chapter Seven: Communications

Overview

Wa t l o w S e r i e s F 4 S / D

C o m m u n i c a t i o n s

■

7 . 1

The Series F4 uses Modbus as its communications

protocol. Modbus is a standard protocol developed

by A.E.G. Schneider. Modbus RTU enables a com-

puter or PLC to read and write directly to registers

containing the controller’s parameters. With it you

can read all of the controller ’s parameters with a

few read commands.

If you already have a software application that us-

es Modbus, the Modbus Registers Table in this

chapter will provide the register number and val-

ues (sometimes called enumerated types) for each

parameter.

Dependencies between parameters do exist. For

best results, program the parameters in the order

in which they appear in the Software Map (inside

back cover).
To program a profile using Modbus, refer to the

Profiling Flow Charts in this chapter.
For basic information about writing an application

using Modbus protocol, you may want to download

the electronic Watlow Controls Data Communica-
tions Guide

from the Watlow web site:

http://www.watlow.com/prodtechinfo
Search on data communications reference.

✔ NOTE:
For ranges, conditions and other information, look up parameter names in

the Index, which will direct you to earlier chapters in this book.

Exception Responses

When a controller cannot process a command it returns an exception response and sets

the high bit (0x80) of the command.
0x01 illegal command
0x02 illegal data address
0x03 illegal data value

Packet returned by controller:

| nn | nn | nn | nn nn |

∆

∆ ∆

controller address (one byte)
command + 0x80
exception code (0x01 or 0x02 or 0x03)
CRC low byte
CRC high byte